1. Field of the Invention
The invention relates to a remote control receiver.
2. The Prior Art
Wireless remote control devices have long been used for distant control of movable objects such as cranes, locomotives, model aircrafts, or toy cars. Such devices are also used with apparatus of the entertainment industry, especially apparatus with increased operating comfort, the different continuously variable adjustments such as sound volume, contrast, color intensity, brightness, and the adjustments variable in discrete steps such as the sender finder, and the station selection, being through wireless remote control. An ultrasonic signal is emitted from a transmitter and is converted into a control signal corresponding to the selected frequency in a receiver section. Besides ultrasonic signals, infrared signals are also used for remote control.
With the use of ultrasonic, different processes are already known. The simplest process is that for each adjustment a special channel with its associated frequency is assigned for characterizing of the kind of adjustment. With a continuously variable adjustment, mostly two frequencies are necessary for changing of the adjustment; that is, a frequency for the increase and a frequency for the decrease of the adjustment. The amount of the desired change is fixed by the duration of pushing an input key. On the receiver side for recognition of the different frequencies, a number of resonant circuits is used corresponding to the number of different frequencies, which makes necessary a time-consuming calibration before putting the receiver into service.
With modern remote control systems using integrated circuit networks, the arriving ultrasonic frequencies are converted into pulses, the pulse repetition frequency of which is equal to the ultrasonic frequency. The pulses received during a fixed time limit are counted in a counter and evaluated. Another known method is the pulse code method. Here, a coded pulse sequence is emitted from the transmitter and decoded in the receiver. This principle has the disadvantage that it is relatively expensive to construct the sender as well as the receiver. A further disadvantage is the poor freedom from interference such that especially at the border of the service radius, or with a weakened transmitter battery, false operation can occur.
With the use of ultrasonic signals there is the disadvantage that interference can occur in the transmission path such that the received ultrasonic oscillations do not correspond with those transmitted, and therefore false operations are produced. These interferences can consist in that, for example, the transmitted ultrasonic oscillations are superposed with ultrasonic oscillations reflected in the room and therefore cancelled. In addition, the ultasonic-wave components of extraneous noises such as key rattling, ringing of a telephone, or the sweep radiations of the horizontal line scan of a television receiver, or other interference sources, such as ultrasonic washing plants or the simultaneous operation of several ultrasonic remote controllers, can produce a false operation. Relatively expensive circuits and transmitting methods have been developed to prevent such false operations.
A remote control device is already known in which a sending oscillator is switched on or off in synchronism with the pulses to be transmitted, and in which the signal generator (transmitter) is a mechanical structure capable of oscillating, that is, a loud speaker, which decays after switching-off the sending oscillator. If it is stimulated for a short time at its resonant frequency, however, uncontrollable oscillations occur which can lead to false operations. Similar difficulties result with the use of receiver microphones which likewise consist of a mechanically oscillating structure. To suppress the influence of the interference oscillations when switching the sending oscillator on and off, it has been proposed to send a first frequency as desired frequency during the pulse duration, and a second frequency as auxiliary frequency during the spacing intervals between the pulses of the first frequency, such that the auxiliary frequency is sent after the last pulse until the receiver is no longer ready to receive, or such that the amplitude of the auxiliary frequency sent after the last pulse is continuously but slowly decreased until no further oscillations containing the desired frequency are produced. A pulse generator producing a pulse sequence is provided which switches the auxiliary frequency on or off with an electronic circuit. From this follows that the sending oscillator oscillates with the desired frequency during the pulse duration instead of with the auxiliary frequency. The number of pulses which are produced by the pulse generator depends upon which one of the keys connected with the pulse generator is operated. The desired frequency is separated from the auxiliary frequency by a resonant circuit in the receiver. A monitoring circuit recognizes whether a desired pulse has been received. If the monitoring circuit recognizes a desired pulse at the beginning of the remote control signal, a monostable sweep stage is triggered. The output of the sweep stage is connected with an electronic switch which then releases the receiver for evaluation. The duration of the astable ON-condition of the sweep stage is chosen such that the circuit is open as long as the transmission of the maximum possible number of pulses lasts. It is disadvantageous with this remote control device that no further operation channel may lie between the auxiliary and desired frequencies, because the oscillator frequency covers the complete range lying between the auxiliary frequency and the desired frequency when the frequency is switched.
Further, an ultrasonic remote control with pulse modulation is known for television sets, in which the ultrasonic signal is composed of two chronologically successive frequencies which are coded in their value and in their respective duration. The frequency of the first ultrasonic tone determines the kind of information, whether, for example, a channel shall be selected or a level shall be changed, while the duration of the first ultrasonic tone fixes the channel number or the kind and direction of the level change. Only the second ultrasonic tone initiates the execution of the command stored previously; its duration controls in digital steps the magnitude of the level change. The ultrasonic signal is amplified in the receiver, limited, filtered, and then converted into direct current signals. Multivibrators are switched on or off by the ultrasonic signal, and produce pulses with an exactly defined period during the intervals that they are switched on. These pulses are evaluated in decadic forward and backward ring counters. Connected to their outputs are additional dircuits wich pass on to the stages to be controlled the digital commands, either directly or converted into analogue value. It is disadvantageous with this remote control device that reverberation effects make an exact evaluation of the transmitted frequency packages impossible.
To avoid false operations caused by interference noises, a remote control arrangement is already known wherein shortly before the actual desired signal a pre-pulse with a longer pulse duration than the desired pulse is sent. The desired signals consist of pulse groups which have a different number of desired pulses according to the television program desired. The transmission takes place in a transmission channel such that a carrier frequency is keyed on and off in the rhythm of the pulses. An evaluation circuit is provided in the receiver which checks whether the received signal contains a pre-pulse at the beginning. The duration of this pre-pulse is long enough that it cannot be simulated by interference signals. Upon recognition of a pre-pulse, a monostable sweep circuit is set, its output controlling the current conduction of an electronic switch. The duration of ON-connections of the monostable sweep circuit is sufficiently long that the maximum possible number of desired pulses can pass through the electronic switch. It is disadvantageous that with short desired pulses the circuit conducts current, so that interferences can trigger false operations. To avoid this disadvantage, it has been proposed to control the monostable sweep circuit with a trigger circuit. The timing element determining the duration of ON-connection of the monostable sweep stage is controlled, that is, reset, when a signal appears at the output of the trigger circuit. The duration of the monostable state is chosen to be smaller than the duration of the longest possible desired signal.
Further, an arrangement for wireless remote control using ultrasonic for plural devices is known which can be remote-controlled by a common transmitter, or by plural transmitters independent of one another. This arrangement is intended for the case when a television set and a stereo receiving device are to be operated in the same room. Because the number of available frequencies is limited, it has been proposed to transmit for each independently controlled receiver an additional identification frequency simultaneously with or interposed in a predetermined way with the unmodulated command frequency. The respective ultrasonic receiver thus reacts only if it receives its own identification frequency in addition to the command frequency. The remaining receivers having identical command frequencies but a different identification frequency are not addressed. If the range of the available ultrasonic frequencies is not sufficient for additional identification frequencies, it has been proposed to use no identification frequency for the first receiver, and to use a command frequency of the first receiver as identification frequency for the further receivers, so that the first receiver does not react if this frequency is received together, or interposed in a predetermined way, with the other command frequency. On the receiver side, resonant circuits are present, for each identification frequency, which make necessary a time-consuming calibration process before placing the device in service. It is further disadvantageous that upon interruption of the ultrasonic signal after the identification frequency, for half a period duration of the ultrasonic signal, a false operation can be triggered by interference frequencies.